The present invention relates to a percutaneous (skin penetrating) bone anchored transferring device and a connecting means, preferably by means of which an outer device can be connected to an inner implanted subcutaneous unit.
In spite of an increasing need for a percutaneous connecting device for permanent use, in particular for the transfer of electrical information and/or electric energy there is no commercially available unit being allowed for clinical use in spite of the fact that there are several patents within the field. It is believed that the reason that these patents have so far not led to any commercial product is probably due to the fact that the patents describe connecting devices which are either too complicated in that they contain too many poles and ingoing components or that they do not attend to all the intricate demands raised from biocompatibility, anatomical, surgical, electrical, patient safety and handling points of view. Some of the published patents in this field are described below.
In U.S. Pat. No. 5,562,670 to Brånemark an electrical connecting device is described which is applied by means of a threaded tubular implant where its inwardly turned end has a central bore. The contact means and the set of cables are introduced and fixed from the outside of the implant. This is a patent by the pioneer and the inventor of titan implants of today concerning dental rehabilitation, bone anchored hearing aids, and face prosthesis, knee and finger joints, etc. When it comes to practical realization of the electric connecting device described in U.S. Pat. No. 5,562,670 there is a weakness in that the implanted set of cables and the inner implanted unit have to be so small that they can pass through the central bore of the implant. For most applications, however, the inner implant is too large to be able to pass through the central bore of the implant. In these cases the units have to be surgically implanted as an integrated unit or become mounted together with the implant in place or become connected by means of a second implanted connecting device that is small enough. If the contact means should be repaired or maintained, which is necessary with regard to the environment that a skin penetrating implant is subject to (contact surfaces become oxidized etc.), this has to be done in the skin penetrating abutment itself. If one should wish to remove/exchange the connecting device the whole implanted set of cables has to be removed. Fixation of the implant using threads has the disadvantage that the bone anchored part of the implant has to have a diameter large enough to encompass the thread, which clearly restricts the possibilities to encompass connecting components therein as well. It is desirable to be able to encompass the connecting components in the bone anchored part of the transferring device to reduce the total height of the transferring device. A well functioning transferring device should not extend outside the skin level more than 1 to 3 mm in order to avoid damages from possible outer mechanical violence and in order that the implant should be experienced as acceptable from an aesthetical point of view. Furthermore, a screw implant has to be rotated during the application which means that an asymmetrical design of the implant is very hard to realize. An asymmetrical design of the implant is desirable as the bone thickness where the implant has to be placed is so thin that the set of cables has to leave the implant in a radial direction. Furthermore, practical problems will result because the inner implanted unit has to rotate together during application if it has been pre-mounted and passes through the transferring device due to the fact that it is too large to be applied afterwards through the bore.
U.S. Pat. No. 3,870,832 to Fredricson discloses a connecting device for the application of a microphone, which device corresponds, in principle, with the Brånemark patent. Fredricson shows that the retention of the microphone element is done using a locking nut which is applied using an outwardly turned thread on the implant. Such design would lead to a potential risk for bacterial accumulation and risk for skin irritation. Additionally, the design according to this patent, is subject to the same weaknesses as described above with reference to patent U.S. Pat. No. 5,562,670.
U.S. Pat. No. 5,604,976 to Stobie et al discloses a connecting device for a great number of conductors, the inner part of which is not intended to be lowered beneath the outer limiting surface of the bone, but instead becomes fixed above the same but below the soft tissue. In this connecting device the set of cables lead to the inner implanted unit on the top of the bone but beneath the soft tissue. Problems reported in clinical tests using such an arrangement shows that the set of cables having a realistic minimum diameter of 1 to 2 mm and being a little elastic creates a biocompatibility problem at the skin penetration area, probably due to the occurrence of small movements between the mobile skin and bone with a foreign material there between. Furthermore, the necessary skin reduction can be jeopardized if the set of cables does not have a very small diameter. The connection can be severed apart by means of tools to loosen a screw connection, but can not, for any reason, be disconnected in daily use. This connecting technique further means that rotation of the outer connecting part is not possible and that the device is not protected from excessive external forces.
U.S. Pat. No. 5,507,303 to Kuzma discloses a connecting device where the implant is anchored to the scull bone but where the skin/bone connecting tissue closest to the implant is separated from the scull bone using a large flange. Experience from skin penetrating titan implants in the scull bone shows that it is of utmost importance that the skin around the penetration area has been adequately reduced in thickness and that the thickness reduced skin is allowed to grow against bone connecting tissue and scull bone (Tjellström, Anders, et al, The Bone Anchored Hearing Aid—design principles, indications and long-term clinical results, Otolaryngologic Clinics of North America, vol 28(1), 1995, pp 53-72). The flange of the actual connecting device hinders the skin from growing to the bone/bone connecting tissue, and the frequency of skin complications can be expected to be relatively high. Furthermore, the whole connecting device is placed outside both the bone and the skin, which means that it will extend a considerable distance above the skin surface. The retention between the connecting parts is done using magnetic force.
U.S. Pat. No. 4,025,964 to Owens discloses a connecting device which unlike the connecting devices above is not anchored to the bone in a stable way. Even small movements of the implant relative to the skin will lead to a great risk for skin irritation. Fixation between the male and female parts of the connecting device is carried out using magnetic attraction force and the parts can not be rotated relative to each other.
U.S. Pat. No. 3,995,644 to Parsons discloses a connecting device as well, which is merely fixed to the skin and intended to transfer an electrical signal, preferably for electrical stimulation of muscle units. Due to the fact that even small movements between skin and implant create irritation, this type of connecting devices should only be used temporarily.
U.S. Pat. No. 4,328,813 relates to a system for anchoring a brain cable and is only intended to geometrically fix or lock a cable such as an electrode for the stimulation of a certain point in the brain. The cable is thereby intended to be brought underneath the scalp to an electric stimulator. As the implant is manufactured in an elastic material, which is provided with slots, the implant can not be used for a bone anchored percutaneous transferring device.
SE-C-503,790 relates to a passive screw implant for the transfer of vibrations from an outer vibrator (loud speaker) to the scull bone. Such an implant can not transfer electrical signals, energy or drugs to the inner body.
Finally, there are a number of connecting devices which are intended to be used totally subcutaneously, such as U.S. Pat. No. 4,495,917 to Byers, but these are so different to the present invention concerning functional requirements and constructive solutions that a further analysis does not seem to be meaningful.
An improved connection/transferring device that is designed for daily use, such that the connection is simple and allows substantially free rotational positioning and that the connection is easily maintained and worn out parts can be simply exchanged, is needed. Furthermore, a connection design is needed that will disconnect if subjected to a large enough outer mechanical force.